Nickel‐Catalyzed Unsymmetrical Bis‐Allylation of Alkynes

Abstract

The catalytic bis-allylation of alkynes is an important but challenging protocol to construct all-carbon tetrasubstituted alkenes. Particularly, the catalytic unsymmetrical bis-allylation of alkynes remains as an underexplored task to date. We herein report an unprecedented unsymmetrical bis-allylation by simultaneously utilizing electrophilic trifluoromethyl alkene and nucleophilic allylboronate as the allylic reagents. With the aid of robust Ni 0 /NHC catalysis, valuable skipped trienes can be obtained in high regio-and stereo-selectivities under mild conditions. Mechanistic studies indicate that the reaction may proceed through a β-fluorine elimination of a nickelacycle followed by a transmetalation step with allylboronate. The present method exhibits a good tolerance of various functional groups. Besides, the skipped triene products can undergo an array of elaborate transformations, which highlights the potential applications of this strategy.

Synthesis of Fluorinated Compounds by Nickel-Catalyzed Defluorinative Cross-Coupling Reactions

“…The Chen group described the nickel-catalyzed three-component bis-allylation of alkynes with trifluoromethyl alkenes and allylboronates as allylic sources, providing an efficient method for the synthesis of valuable skipped trienes 179 with excellent regio- and stereoselectivity (Scheme ). Mechanistic studies suggest that the reaction is initiated by the oxidative cyclometalation of alkyne, trifluoromethyl alkene, and Ni(0) to generate nickelacycle intermediate 180 . β-Fluorine elimination of intermediate 180 gives alkenylnickel intermediate 181 , which undergoes transmetalation with allylboronate to furnish nickel­(II) species 182 .…”

Electronic Asymmetry Engineering of Fe–N–C Electrocatalyst via Adjacent Carbon Vacancy for Boosting Oxygen Reduction Reaction

“…It shows that high electron density of the Fe─N 4 structure causes an excessively strong binding of the oxygen intermediates, which is caused by an upshifting of the d z2 metal orbital and an increase in the molecular hardness, or the distance between d z2 and the molecular oxygen energy level, but the asymmetric electronic density of the Fe─N 4 Vc structure optimizes the adsorption toward O 2 and the intermediates and thus lowers the energy barrier for ORR. [51] Figure 4d and Figure S34 (Supporting Information) display the Gibbs free energy profile of ORR catalysis steps on different structures at U = 0 V. Both the normal Fe─N 4 moieties and Fe─N 4 Vc structures showed a consistent downhill energy pathway, indicating a thermodynamically favorable process on their surfaces. At a potential of 1.23 V, however, the rate determination steps (RDS) of the Fe─N 4 and Fe─N 4 Vc structures presented an uphill free energy profile ascribed by the fourth electron transfer step (*OH + e − → OH − ).…”

Recent Advances in Nonprecious Metal Catalysis

“…Like Koh, Gutierrez, and co-workers, two additional three-component methods were reported; however, instead of generating quaternary centers, these reactions produced difficult-to-access tetrasubstituted alkenes stereoselectively (Scheme ). The process designed by Wang, Zheng, and co-workers uses aryl boronic acids, aldehydes, and alkynes to produce allylic alcohols (Scheme A). Conditions were screened to avoid generating the reductive coupling and 1,2-addition products, resulting in excellent ( Z )-selectivity.…”